This is a nationalization of PCT/SE00/00734 filed Apr. 17, 2000 and published in English.
The invention relates to an antenna means for transmitting and/or receiving RF signals, comprising a conductive structure extending between first and second opposite edges and a feed portion. Specifically, it relates to an antenna means for a mobile radio communication device, and is especially suitable as a vehicle antenna. It also relates to a radio communication system including such an antenna means and to a method for manufacturing a radiating structure included in the antenna means.
Many vehicles are equipped with antennas protruding from the vehicle body. Such antennas are for example whip, wire or blade antennas. To overcome problems with elements protruding from the vehicle body, there is a demand for antennas concealed or arranged in the vehicle.
U.S. Pat. No. 5,682,168 discloses an example of such antennas, where a dipole antenna is submerged beneath a cover over a roof supporting member of a motor vehicle or hidden behind or as a part of the front grill. In U.S. Pat. No. 5,402,134 a planar antenna for installation under a dielectric cover of a vehicle is disclosed. Antennas concealed in a piece such as a spoiler rack are disclosed in U.S. Pat. No. 5,629,712 and U.S. Pat. No. 5,812,095. Those antennas are complicated to manufacture and to mount. Further, operation in more than one frequency band requires special arrangements. They are also dependent of a ground plane or sensitive to conductive parts in the vicinity.
Further, U.S. Pat. No. 5,177,494 discloses a vehicular slot antenna system, in which a plurality of slot antenna units are installed on the vehicle. Each antenna unit is U-shaped and is provided with a closed opening or slot. Such an antenna unit is intended for operation in one frequency band only. Further, an antenna unit of this kind radiates from both sides of a plane of the plate portion in which the slot is arranged.
The main objects of the invention are to provide an antenna means for transmitting and/or receiving RF signals, which antenna means can be manufactured in a simple and cost-effective way, is simple to mount and requires a relatively small space.
Another object of the invention is to provide an antenna means, which, does not require a separate ground plane and can be mounted to have relatively low sensitivity to adjacent conductive parts.
These and other objects are attained by an antenna means.
By the features of an antenna means, which can operate in more than one frequency band, is achieved.
By the features of an antenna means having good antenna performance and directional radiation characteristics is further achieved. The arrangement of the radiating structure as a closed structure has the effect that a main portion of the radiation is directed from the slit portion in a lobe away from the radiating structure. Mounted in a vehicle with the slit facing a glass pane, thus a major portion of the radiation will exit through the window in directions from the vehicle.
The antenna means does not require a separate ground plane and can be mounted to have relatively low sensitivity to adjacent conductive parts, is very suitable for mounting a vehicle with the slit covered by a glass pane, and the radiating structure adjacent to, or far from conductive parts.
By providing the slit with open ends the operation in plural bands is remarkably improved, and surprisingly it also makes it possible to decrease the dimensions of the antenna means without significant decrease in antenna performance.
By the features of an antenna means which is simple to match, and in which the matching can be done directly in the radiating structure, is also achieved.
By the arrangement of a capacitance between the edges of a slit, the electrical lengths in the radiating structure are increased, and therefore the dimensions of the antenna means can be reduced.
By forming the capacitance by portions of the conductive structure, a well defined capacitance, which can be formed in a simple and efficient way is achieved.
By the arrangement of a second slit, the antenna characteristics in a higher frequency band can be further improved.
By the arrangement of a dielectric material covering the slit, the electrical lengths in the radiating structure are increased, and therefore the dimensions of the antenna means can be reduced.
By further arranging the antenna means having a dielectric material covering the slit to be covered by a second dielectric material having different dielectric constant, such as a window, the electromagnetic waves transmitted/received by the antenna means can be refracted and the antenna lobe can hereby be controlled.
By including a conductive layer carried by a dielectric substrate or carrier in the conductive or radiating structure, an antenna device is obtained, which is simple to manufacture with simple, suitable and accurate methods for obtaining the slit.
By dividing the conductive or-radiating structure into at least two constructional portions, whereof one portion includes a conductive layer carried by a dielectric substrate or carrier, an antenna device is obtained, which is simple to manufacture and to adapt to different frequency bands and operation conditions.